i call them mexican onions the onion drops of when ready and roots in the soil i think the would grow in any kind of soil not to dry and full sun

I found out about this plant from an old herb book and I'm looking out for one. They call it a Tree Onion (Egyptian Onion), Allium cepa, var. proliferum.
It doesn't help with garden situation but says to grow some young onions in a pot on the kitchen windowsill for 'winter onion green over a long period'.